The present invention relates to virtual fences and, in particular, it concerns an active virtual fence using mesh networked RF Tags.
There are many security applications in which a sensitive area must be protected from intruders. A conventional approach is a wall or a fence. However, advances in current technological allow the use of an electronic fence or virtual fence which senses the presence of unwanted activity in the protected area and usually generates a warning.
Current approaches for building a virtual fence include placing an array of control towers, each equipped with movement detection and security radar, cameras or motion detectors. Such as the systems disclosed in U.S. patent application Ser. No. 2006/0033617 to Wakefield and U.S. Pat. No. 4,124,848 to Clark, et al. A similar system was described at the beginning of 2007 by the US Department of Homeland Security with regard to awarding aerospace giant Boeing a contract to provide high-tech methods to catch illegal immigrants along the U.S.-Mexico border. Boeing's “virtual fence” concept includes an estimated 1,800 towers deployed along the border and equipped with cameras and motion sensors. The cost of this project is about 10 billion dollars.
Another approach offered by some companies is a Virtual Fence Passive Multi-Sensor System, which includes a covert, passive device designed to detect human activity independent of a physical obstacle. This Virtual Fence is a sensor array, combining acoustic, seismic and infrared (IR) sensors to detect, locate, and identify human activity in a protected area. The system enables target detection beyond line of sight, such as movements of humans, vehicles and low flying helicopters hidden in ground defilades.
In such a system, the sensors are installed underground, in sealed boxes containing digital signal processors and wireless communications devices, geophones, microphones, IR detectors and power sources. The only element above ground is a concealed camouflaged antenna and IR detector. Each sensor contains a processing unit which performs target identification (ID) and direction finding (DF). The IDDF algorithms enable monitoring and discriminating between diverse activities, such as moving humans, digging and building work, as well as mechanical noises such as approaching vehicles. The system can be implemented to provide early warning for border and perimeter control, tunnel excavation, protection of pipelines and electrical infrastructure, guarding vital installation perimeters as well as monitoring prison fences.
Other previous art virtual fence techniques have been described in U.S. Pat. No. 6,067,044 Whelan, et al., and U.S. Pat. No. 6,342,847 to Archuleta, et al., and U.S. patent application Ser. No. 2006/0197672 to Talamas et al. and No. 2006/0238340 to Harvey. These virtual fences use GPS to determine if a tagged object is outside an allowed boundary. The GPS is used to measure the location of the object and this location is compared to a threshold defining the perimeter of the virtual fence.
Other patents suggest the use earth based transmitters for locating an object. Examples include U.S. patent application Ser. No. 2004/0108939 to Giunta in which the device uses both GPS as well as earth based transmitters to locate itself. U.S. Pat. No. 6,353,390 to Beni et al. uses cellular base stations for location. U.S. patent application Ser. No. 2007/0257831 to Mathews et al. uses CDMA signals from earth based transmitters. U.S. Pat. No. 6,720,881 to Halliday describes a wearable transmitter, an alarm condition is detected when the transmitter, is detected by some receivers in the perimeter. All these solutions require that the tracked object/person will carry a special unit used for location. This requirement is not feasible in security applications in which the objective is to determine the presence of a foreign intruder.
Other suggested techniques for creating a virtual fence include using laser beam or infrared light, such as in U.S. patent application Ser. No. 2007/0012901 to Mikuski et al. and U.S. Pat. No. 6,985,212 to Jamieson et al. in which a fence using infrared light is made, such that an intruder is detected if the beam is broken. Such approaches are possible only for short distance over flat terrain and are dependent on weather conditions.
Two other proposed solutions are provided in U.S. patent application Ser. No. 2005/0147340 to Tapanes that describes fibers that are buried in the ground to detect when there are being stepped on, and U.S. patent application Ser. No. 2004/0113780 to Pottratz which suggests tripwires to detect crossing.
There is therefore a need for a virtual fence using mesh networked RF Tags.